Question Memory: CPU compatibility?

I want to upgrade my pc with a new MB, a new CPU and new memory. However, when looking at the supported frequency of the MB I want to buy ( B450 Gaming K4/index.asp#Specification) it says that the supported frequency is dependent on the CPU series. I always thougth that those were complete loose from each other
The memory controller is located on the CPU and with each iteration of Ryzen has been improved over the older generations. This means that the Ryzen 3000 series has the highest official RAM speed support, 2000 series is in the middle, and 1000 series is the lowest.
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